The current version of Team Developer (TD) out now is v4.2, so I doubt
that
any VAR or other source would still have 2.1 for sale. I'm sure that
is also
true for Unify, the company which now owns the 'Gupta' products.

re your "what's the difference" question: there isn't one. TD has gone
through
quite a few name changes over the years since its release in 1988;
here's a
little summary that might help. It has a couple guesstimates but
should be
fairly accurate:

1988 - Gupta Technologies, Inc. released the original SQLWindows
product, a 16-bit application

~1990 - Gupta Tech. name change to Gupta Corporation

~1994/5 - SQLWindows v5 out, the last of the 16-product

~ mid/latter-90s - Gupta Corp. name change to Centura Corp.
SQLWindows name change to Centura Team Developer (partily because
it became a 32-bit appl.)

~early 2000s - back to being called Gupta Corp.
Centura TD name change back to Gupta Team Developer or just "Team
Developer"

2006 - Gupta tried to release a TD v5, that was bad product and was
withdrawn

~200t Gupta bought by Unify. Product now referred to as Team Developer

2007 - latest/current release: Team Developer v4.2

2007 - Unify announces it will be coming out with a revamped TD,
called TD v5.1 this fall some time

if you want to buy TD 2.1 licences maybe i can help you. How many do you
need? The company in which i still working is a gupta licence partner. So if
you have interest i can make you a good offer. However it is a germany
company but i think that makes no different for you.